Idea #7: Local Note Encryption

Joplin’s end-to-end encryption protects notes during sync, but not on the local device. This project adds local note encryption so users can lock sensitive notes behind a vault password while preserving compatibility with sync and existing E2EE. The implementation will use an option-gated save/load flow, on-demand decryption, protection against plaintext leaks through search and revision history, and a lock screen UI for desktop. Guaranteed deliverables are a working desktop implementation, vault password management, sync/backward-compatibility support, and tests for data-safety and conflict handling. Stretch goals include mobile support, resource encryption, and CLI/Data API integration.